Extracting Square Roots Made Easy: A Little Known Medieval Method - Appendix: When Was Fermat Born?

Editor's note: As of 2016, an expanded version of this appendix now appears as the separate article, When Was Pierre de Fermat Born? The expanded article includes a photograph of Fermat's gravestone with the inscription reading that Fermat died in 1665 at the age of 57 years.

Most biographies of Fermat still give 1601 as his birth year. However, Klaus Barner, Professor Emeritus of the University of Kassel, Germany, has discovered that this is incorrect (2001). Investigating in French archives, he found the following facts: In the baptismal register of the city of Beaumont, he read that Piere (with one “r”), son of Dominique Fermat, was baptized August 20, 1601. Other documents show that the name of Piere's mother was Françoise Cazenove. It seems that she, her son, and a daughter died after 1603. Sometime between 1603 and 1607, Dominique Fermat married a second time. His new wife, Claire de Long, bore him five children, among them a son named Pierre again, like his deceased half-brother. Unfortunately the baptismal registers from 1607 to 1611 are completely missing. But the mathematician's eldest son, Samuel, had written in the Latin epitaph of his father at the family grave in Toulouse:

OB.[iit] XII. IAN[uarii] .M.DC.LXV. AET[ate] .AN.[norum] .LVII.

That is, Pierre de Fermat died on January 12, 1665, at the age of 57 years. This means he was born between January 13, 1607, and January 12, 1608, and most probably in 1607. Additional research led Barner to conclude that Fermat was born between October 31 and December 6, 1607 (2007). In 1631 Fermat was conferred the right to add the title of nobility "de" to his name.